Do objects launched from Earth retain the Earth's lateral inertia (67,000mph).

We've probably all heard of the gun on a train theory. Fire a bullet that would normally travel 500mph on a train that's moving 200mph (in the same direction the train is moving) and you've now got a bullet going 700mph.

Please find my basic diagram attached above.

So if the Earth is moving through our solar system at 67,000mph, would an object shot from Earth, precisely 90° from the Earth's current rotation path continue to travel at 67,000mph "sideways/laterally" relative* to other "stationary" objects in the solar system. EG, is it now travelling 67,000mph sideways and also 1,000mph forwards (Hypothetically assuming it lost no energy escaping the Earth's atmosphere here).

*By relative, I mean, relative to the sun - exact same distance and static rotation path.

One of the situations that made me think of this is the Voyager1 spacecraft. Did the Voyager1 have to do any special adjustments to escape the lateral inertia of 67,000mph or did it just use it to its advantage?

  • $\begingroup$ The voyager was helped by this, otherwise it would have fallen into or near the sun and gotten incinerated. Orbital mechanics are more complex when you consider the influence of the suns gravity, but it still starts out with the 67k boost. $\endgroup$ Jan 8, 2015 at 1:17

1 Answer 1


Yes, objects launched from an orbiting body such as a planet inherit the velocity of that body at the time they're launched. They could hardly do anything else without violating conservation of momentum. :)


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